Ethernet communications provide high speed data communications over a communications link between two communications nodes that operates according the IEEE 802 Ethernet Standard. The communications medium between the two nodes can be twisted pair wires for Ethernet, or other types communications medium that are appropriate. Power over Ethernet (PoE) communication systems provide power and data communications over a common communications link. More specifically, a power source device (PSE) coupled to the physical layer of the first node of the communications link provides DC power (for example, 48 volts DC) to a powered device (PD) at the second node of the communications link. The DC power is transmitted simultaneously over the same communications medium with the high speed data from one node to the other node.
Example PD devices that utilize PoE include Internet Protocol (IP) phones, wireless access points, etc. The PSE device typically includes a serial-to-parallel (i.e. SERDES) transceiver, and/or a PHY device, to support high speed serial data transport. Herein, data ports and their corresponding links can be interchangeably referred to as data channels, communication links, data links, etc, for ease of discussion. The PSE device also includes a PSE controller that performs initialization and power flow control to the PD device.
PoE integrated circuits are sensitive to electrostatic discharge (ESD). ESD occurs when a static charge discharges. The static charge may have a high voltage of several thousand kilovolts. When the ESD voltage exceeds a spark gap voltage of an insulator, the electrostatic charge discharges through the insulator in an ESD event.
An ESD event may occur during handling of the PoE integrated circuit, such as during a manufacturing process. An ESD event may also occur during normal operation of a PoE integrated circuit. For example, an electrostatic charge on a cable may discharge via a PoE integrated circuit port during connection of a cable to the port.
An ESD event may render an unprotected PoE integrated circuit inoperative by destroying layers of a sensitive internal circuit. PoE integrated circuits are miniature in size. Spark gap voltage decreases as insulator thickness decreases. Thus, PoE integrated circuits tend to be susceptible to damage due to ESD events.
Some PoE integrated circuits have a conventional ESD protection circuit to combat detrimental ESD effects. Unfortunately, when managing an ESD event affecting only one port, conventional PoE ESD protection circuits cause a loss of operation on all ports. Thus, cable systems having multiple ports are particularly vulnerable when one port has a ESD event. Conventional ESD protection circuits also cause a loss of power supplied to the PD when managing an ESD event.
Thus, what is needed is an ESD protection circuit for PoE devices that overcomes the shortcomings described above.